Differential stimulation of pancreatic-polypeptide and gastrin secretion by bombesin in man

Bombesin, besides many other actions on the mammalian gastroentero-pancreatic tract, strongly stimulates the release of pancreatic-polypeptide (PP) in dogs. In 8 healthy human volunteers (5 males, 3 females), the PP response during bombesin infusion was low (25.7 ± 6.3 peak vs. 5.0 ± 2.0 basal pmol/1) compared to the effect of a protein meal (144.1 ± 13.4 pmol/1) or to the gastrin response to the same dose of the amphibian polypeptide (140.0 ± 23.6 pmol/1 eq SHG 17 I). The response pattern of PP and gastrin was different as PP concentrations peaked 10 min after cessation of bombesin infusion (32.0 ± 4.9 pmol/1) when gastrin concentrations already were down to one third of the maximal response. Atropine inhibited the PP response to bombesin but did not abolish it completely. It is concluded that in man, the total effect of bombesin on PP secretion is minor compared both to the effect of the peptide on gastrin secretion in man and to the effect of bombesin in dogs. It is suggested that bombesin might have a dual, inhibitory-stimulatory, effect on PP secretion in man.     

Effect of truncal vagotomy on pancreatic polypeptide response after intravenous glucose administration

Intravenous glucose infusion was performed in six dogs with and without truncal vagotomy, and plasma pancreatic polypeptide (PP) responses were compared before and after truncal vagotomy. Following truncal vagotomy, basal PP levels decreased significantly from 286 ± 64 pg/ml (mean ± S.E.) to 94 ± 14 pg/ml (P < 0.05). Basal plasma insulin and blood glucose levels also tended to be lower, but not significantly. During the influsion of glucose, blood glucose concentrations rose rapidly in both groups and after 15 min reached peak values which were not significantly different from each other. In the vagotomized group the plasma insulin response to intravenous glucose infusion was significantly lower than in the control group. Following intravenous glucose loading, plasma PP concentrations decreased rapidly in both groups, but the PP level in the vagotomized group was suppressed only to 77 ± 4% of the basal level whereas in the control group it decreased to 45 ± 8%, significantly lower than in the vagotomized group (P < 0.01).These results suggest that basal PP is regulated by vagal tonus and that vagus controls, at least in part, suppression by intravenous glucose administration.     

The influence of cadmium (CdCl2) on the canine plasma levels of gastrin,cholecystokinin (CCK), and pancreatic polypeptide (PP)

The influence of cadmium on basal and stimulated plasma levels of gastrin, cholecystokinin (CCK), and pancreatic polypeptide (PP) was investigated in conscious dogs using three doses of cadmium (0.15, 0.5, and 0.75 mg Cd/kg-h). Levels of gastrointestinal (GI) hormones were stimulated with bombesin (BBS), a peptide known to stimulate GI hormone release. Plasma cadmium was measured employing atomic absorption spectrophotometry and GI hormone levels were measured with specific radioimmunoassays (RIA). Basal plasma levels of hormones (pg/mL) in the dogs were in the range (mean ± SE): 38±5 to 44±6 for gastrin, 80±25 to 107±17, for CCK and 120±5 to 142±5 for PP; these levels did not change with cadmium. Significant increases above basal levels in all three hormones were found with infusions of BBS and with BBS plus cadmium. Gastrin levels remained steady during Cd and saline after BBS; however, CCK and PP levels dropped to values that were 68 and 73% less than their stimulated peak levels. With reinfusion of BBS, gastrin, CCK, and PP were significantly elevated above basal; however, the peak values for CCK and PP, but not gastrin, were less than those found during the first BBS infusion. The data suggest that in response to bombesin, cadmium has little or no effect on the release of gastrin, but that is exerts a latent effect on the release of both CCK and PP.     

Cholinergic inhibition of meal stimulated plasma neurotensin like immunoreactivity in man

Meal stimulated plasma neurotensin like immunoreactivity (NTLI) was compared during saline or atropine infusion in six volunteers over six hours. Plasma gastrin and pancreatic polypeptide were also measured to compare the timing of their release to that of NTLI. Like plasma gastrin and PP, plasma NTLI rose rapidly following the meal, rising from 27±7 pmol/1 to a peak of 45±8 pmol/1 at 20 minutes (p < 0.05). Also, like that of pancreatic polypeptide, the release of NTLI was biphasic. Sixty minutes after the meal, plasma NTLI had returned to basal values, followed by a rise to a prolonged peak of 64±10 pmol/1 between 90–180 minutes (p < 0.05) returning once more to basal values by 240 minutes. Following atropine, basal plasma NTLI fell from 22±4 pmol/1 to 11±2 pmol/1 (p < 0.05), but rose to basal levels 30–60 minutes after the meal, where it remained unaltered for the remainder of the study. We conclude that both basal and meal stimulated plasma NTLI are inhibited by cholinergic blockade. Further, the similar temporal relationship between plasma NTLI and pancreatic polypeptide in the late phase of the meal response, suggests that a component of NTLI may mediate part of the intestinal phase of pancreatic polypeptide release.     

Influence of salicylic acid and methyl jasmonate elicitation on anthocyanin production in callus cultures of Rosa hybrida L.

This study was undertaken to investigate the effects of salicylic acid (SA) and methyl jasmonate (MeJA) on anthocyanin induction, biomass accumulation, and color value (CV) indices for both pigment content (PC) and pigment production (PP) in callus cultures of Rosa hybrida cv. Pusa Ajay. A concentration-dependent response was exhibited by cultures on SA and MeJA at different concentrations individually or in combinations to Euphorbia millii medium supplemented with 204.5 mM sucrose, 2.45 μM indole butyric acid and 2.33 μM kinetin. There was positive influence on both callus biomass and anthocyanin accumulation. Treatment with 0.5 μM MeJA was most effective in inducing anthocyanin biosynthesis in callus cultures. Anthocyanin accumulation in callus cultures was enhanced with the addition of SA and MeJA, but these did not differ significantly from control for the number of days required for pigment initiation and for color intensification. Moreover, the addition of 0.5 μM MeJA alone resulted in a higher frequency of color response (97.25 %), PC (3.48 ± 0.07 CV g^?1 FW), and PP (1.56 ± 0.03 CV test tube^?1) over control. In contrast, the presence of higher levels of SA (400 μM) and MeJA (5.0 μM) reduced frequency of color response, as well as levels of PC and PP. MeJA did not increase biomass accumulation but promoted frequency of color response, PC and PP. Hence, it was suggested that 0.5 μM MeJA promoted anthocyanin production in rose callus cultures. Significant correlation was found between frequency of response and each of the PC (r = 0.988) and PP (r = 0.990). Furthermore, PC and PP were also highly correlated (r = 0.998).     

PP and PT Intervals and TP Segment in Human Electrocardiogram under Experimental Acute Normobaric Hypoxia

Seven male volunteers aged 22–27 years took part in the laboratory experiment for the determination of body response to acute normobaric hypoxia where they inhaled an oxygen–nitrogen gas mixture (9% of О₂) for 25 min. At least 100 cardiac cycles at each of six experimental time points have been recorded by using an electrocardiogram (ECG) recording technique in standard lead II. Mean heart rate (±SD) before hypoxia was 64 ± 2 bpm; the duration of the PP interval was 0.94 ± 0.07 s, that of the PT interval was 0.51 ± 0.02 s, and that of the TP segment was 0.41 ± 0.07 s. Five minutes after hypoxia, it has been found that heart rate (HR) increased by 19%; the duration of the PP and PT intervals and TP segment decreased by 16%, 6%, and 30%, respectively. Twenty minutes after hypoxia, all the parameters reached their initial values. Five and fifteen minutes after hypoxia, HR reached 59 ± 3 bpm; PP interval and TP segment increased by 9% and 14%, respectively, compared to the initial values; PT interval was the same as the initial value at the baseline. The correlation coefficient r_p (PP/PT) was 0.10–0.54; r_p (PP/TP) was 0.94–0.99. The intervals PP and TP were found to be identical.     

Central but Not Peripheral Glucocorticoid Infusion in Adrenalectomized Male Rats Increases Basal and Substrate‐Induced Insulinemia through a Parasympathetic Pathway

Objective: Glucocorticoids acting through the central nervous system are postulated to play a role in the hyperinsulinemia and increased adiposity of obesity. We investigated the role of parasympathetic activation in glucocorticoid‐induced hyperinsulinemia. Research Methods and Procedures: Plasma pancreatic polypeptide (PP) levels were used as an index of parasympathetic output. Insulinemia and plasma PP levels were measured basally and after intravenous glucose injection (300 mg/kg) in adrenalectomized male rats infused with dexamethasone (7.5 μg/kg per day) intracerebroventricularly (ICV) or subcutaneously (SC) for 3 to 6 days in the presence or absence of acute atropine blockade (1.0 mg/kg). Food intake was controlled between groups. Results: Compared with normal rats, adrenalectomy decreased white adipose tissue depot weights and leptinemia, and these were restored to normal values by ICV but not SC dexamethasone infusion. Adrenalectomy significantly reduced insulinemia below normal levels, which was restored by SC dexamethasone replacement. However, ICV dexamethasone replacement increased insulinemia of adrenalectomized rats to levels higher than normal control values (basal, 500 ± 40 pM vs. 280 ± 40 pM; 1‐minute postglucose, 2500 ± 180 pM vs. 1240 ± 260 pM; p < 0.0001) and increased plasma PP levels, which were correlated with insulinemia. Atropine significantly reduced plasma insulin and PP to levels similar to normal controls but had no effect in any other group. Discussion: These data show that glucocorticoids act within the brain to increase insulinemia, most likely through activation of parasympathetic efferent fibers. Such an affect would contribute to the adipogenic effects of central glucocorticoids.     

Cimetidine inhibits the pentagastrin-induced release of calcitonin in normocalcaemic man

Pentagastrin stimulates the release of calcitonin from normal C-cells in the human thyroid. In the present investigation the effect of cimetidine on the liberation of calcitonin in response to intraarterial pentagastrin (0.6 μg · kg^?1) was studied in 14 normocalcaemic patients undergoing surgery for thyroid adenomas. Cimetidine was administered as a bolus injection of 200 mg followed by an intravenous infusion of 1.5 mg · kg^?1 · h^?1. In seven patients not given cimetidine, mean calcitonin concentration in the thyroid vein rose from 419 ± 58 to 2787 ± 645 pM in response to pentagastrin. In seven patients given cimetidine, mean calcitonin concentration only increased from 107 ± 33 to 166 ± 51 pM after pentagastrin. The difference between the two groups was statistically significant both during basal conditions (P < 0.001) and in response to pentagastrin (P < 0.01). The results suggest that pentagastrin affects normal C-cells via release of histamine and that cimetidine markedly interferes with this mechanism.     

Differences in nitric oxide production in porcine resistance arteries and epicardial conduit coronary arteries

The purpose of this study was to test the hypothesis that endothelial cells from resistance arteries and epicardial conduit coronary arteries differ in their expression of nitric oxide synthase (NOS) and calcium metabolism, and that these differences contribute to the mechanism underlying disparate physiological vasodilator responses observed between the two populations of vessels. The functional vasodilator responses of isolated resistance arteries and epicardial conduit coronary arteries were compared in vitro using both the receptor-independent agonist A23187 ionophore to increase intracellular calcium and the receptor-dependent agonist bradykinin. Constitutive NOS (cNOS) activity in monocultures of endothelial cells derived from resistance arteries and conduit arteries was assayed using a fibroblast-reporter cell method. Intracellular calcium concentration was assessed using fura-2 microfluorometry. Nitric oxide production was determined using a chemiluminescence technique, while cNOS protein was quantitated by Western blot analysis. A23187 was a less potent vasodilator of resistance arteries studied in vitro, compared to epicardial conduit arteries (EC₅₀ = 1.6 μM, resistance artery vs. EC₅₀ = 0.03 μM, conduit artery); however, bradykinin was more potent in resistance arteries (EC₅₀ = 0.3 nM, resistance artery vs. EC₅₀ = 2 nM, conduit artery). In pure monocultures of endothelium, nitric oxide production measured by chemiluminescence both basally and in response to A23187 was significantly less in resistance arteries (6.1 ± 0.5, basal vs. 10.80 ± 0.55, stimulated nmol/μg protein), compared to conduit arteries (7.7 ± 0.5, basal vs. 17.00 ± 1.52, stimulated nmol/μg protein; P < 0.05 resistance artery endothelium vs. conduit artery endothelium). cNOS enzyme activity assessed by cGMP production in reporter cell fibroblasts was also lower in resistance arteries compared to conduit arteries (0.17 ± 0.03 vs. 0.33 ± 0.05 fmol cGMP/μg protein, respectively; P < 0.05 resistance artery endothelium vs. conduit artery endothelium). Conduit arteries expressed 2.1 × more cNOS protein than resistance arteries, as assessed by Western blotting of cellular homogenates. No significant differences were found with microfluorimetry in either basal or ionophore-stimulated intracellular calcium concentrations. The results signified that porcine resistance arteries expressed less NOS and produced less nitric oxide than epicardial conduit arteries both basally and in response to an increase in intracellular calcium. This difference was reflected functionally as a decreased vasodilatory response to increased intracellular calcium in resistance arteries that could not be explained on the basis of differences in the metabolism of intracellular calcium. In contrast, the functional vasodilator response of intact vessels to a receptor-mediated agonist was enhanced in resistance arteries compared to conduit arteries, suggesting an important role of signal transduction mechanisms in specific physiological responses. Thus, the ability of the endothelium to regulate on a regional basis the expression of NOS and integrate receptor-mediated responses with these differences may provide a mechanism for diverse vasomotor responses in different populations of vessels. © 1996 Wiley-Liss, Inc.     

Acetylcholine potentiation of field stimulated rat vas deferens: A pre-synaptic muscarinic mechanism?

Acetylcholine (ACh) was found to markedly enhance the nerve stimulation induced twitch response of isolated, field-stimulated rat vas deferens (RVD). The ED₂₀₀ (concentration which enhances the twitch response to 200% of control) for this potentiation was 6 × 10^?6M with the maximum twitch response being increased by more than 3 fold (325 ± 30%). Carbachol (ED₂₀₀ = 8.5 × 10^?7M) showed identical results. With each drug the potentiation was competitively antagonized by atropine (10^?7?10^?5M). Physostigmine 10^?8?10^?6M) both enhanced the basal twitch response (215 ± 8% of control at 10^?5M) and the sensitivity of the RVD to ACh (ED₂₀₀ = 3.3 × 10^?7M) but not to carbachol. Atropine, on the other hand reduced the basal twitch response by 18 ± 3% at 10^?5M. Hemicholinium (10^?4M) also reduced the basal twitch responses by 23 ± 5%. ACh (10^?7M?10^?5M) did not modify the responses of unstimulated RVD to norepinephrine or KCl suggesting a pre-synaptic site of action. Taken together these results are compatible with the presence of a pre-junctional, excitatory muscarinic mechanism in the field stimulated RVD. That this cholinergic system may be of physiological significance is supported by the observations that atropine and hemicholinium depress while physostigmine enhances the twitch response in the absence of exogenous ACh.     

Hepatic-dependent and -independent insulin actions are impaired in the obese Zucker rat model

Objective: Whole‐body insulin sensitivity (IS) depends on a hepatic pathway, involving parasympathetic activation and hepatic nitric oxide (NO) production. Both atropine and N‐monomethyl‐l ‐arginine (l ‐NMMA, NO synthase inhibitor) induce insulin resistance (IR). IR is associated with obesity. Because NO action was shown to be impaired in animal models of obesity, such as the obese Zucker rat (OZR), we tested the hypothesis that the hepatic‐dependent pathway is diminished in OZR, resulting in IR. Research Methods and Procedures: Lean Zucker rats (LZRs) were used as OZR controls. IS was evaluated in terms of glucose disposal [milligrams of glucose per kilogram of body weight (bw)]. Two groups were submitted to two protocols. First, a control clamp was followed by a post‐atropine (3 mg/kg intravenously) clamp. Second, after the control clamp, l ‐NMMA (0.73 mg/kg intraportally) was given, and a second clamp was performed. Hepatic‐dependent IS was assessed by subtracting the response after atropine or l ‐NMMA from the basal response. Results: In the first protocol, basal IS was lower in OZR than in LZR (OZR, 73.7 ± 14.2; LZR, 289.2 ± 24.7 mg glucose/kg bw; p < 0.001), and atropine decreased IS in the same proportion for both groups (OZR, 41.3 ± 8.0%; LZR, 40.1 ± 6.5%). Equally, in the second protocol, OZR presented lower IS (OZR, 79.3 ± 1.6; LZR, 287.4 ± 22.7 mg glucose/kg bw; p < 0.001). l ‐NMMA induced IS inhibition in both groups (OZR, 48.3 ± 6.6%; LZR, 46.4 ± 4.1%), similar to that after atropine. Discussion: We show that the IR in OZR is due to similar impairment of both hepatic‐dependent and ‐independent components of insulin action, suggesting the existence of a defect common to both pathways.     

Influence of suckling status and type of birth on serum hormone profiles and return to estrus in early-postpartum spring-lambing ewes

Twenty-three mature, spring-lambing, fine-wool ewes of Debouillet × Rambouillet breeding were allotted at parturition to one of four treatments which were arranged in a 2 × 2 factorial design with groups representing number of lambs born (i.e., one or two) and suckling intensity (i.e., lambs were weaned at 2 d of age or lambs remained with dams). Beginning at 0900 h on Day 2, 9, 16, 23, and 30 post partum (PP), jugular blood samples were collected from each dam at hourly intervals for the ensuing 6 h. Additional jugular blood samples were collected daily (Days 2 through 30). Animals were observed twice daily for signs of estrus using vasectomized rams. Interval from parturition to estrus (mean ± SEM) was similar (P > 0.15) in ewes nursing their offspring (117 ± 6 d) and those that had their lambs removed (124 ± 6 d). Dams producing single lambs returned to estrus in 126 ± 5 d compared with 116 ± 5 d (P > 0.15) for ewes producing twins. Serum luteinizing hormone and progesterone were low (< 1.7 and 0.5 ng/ml, respectively) in all ewes during the first 30 d PP. Serum insulin did not differ (P > 0.10) between suckled dams and those that had their lambs removed, but ewes giving birth to single offspring had higher (P < 0.05) insulin levels on Days 16 and 30 PP (543 ± 73 and 578 ± 57 pg/ml, respectively) than did dams producing twin lambs (324 ± 73 and 361 ± 57 pg/ml, respectively). Serum growth hormone (GH) did not differ (P > 0.40) between suckling intensity groups on Day 2 PP; however, by Days 16, 23, and 30, ewes in the suckled group had more (P < 0.05) GH than did those producing single offspring (5.4 and 3.6 ± 0.4 ng/ml, respectively). Early removal of lambs in spring-lambing ewes did not shorten the interval from parturition to estrus.     

Effect of sport practice and warm-up duration on the morning–evening difference in anaerobic exercise performance and perceptual responses to it

This study was designed to assess the effect of sport practice and warm-up duration on the morning–evening differences in muscle power and fatigue during performance of anaerobic exercise and perceptual responses to it. Twenty-two male physical education students – twelve trained (TG) (21.51 ± 1.25 years, 182.17 ± 4.37 cm and 82.88 ± 11.23 kg) and ten untrained (NTG) (23.89 ± 3.17 years, 176.8 ± 2.2 cm and 82.24 ± 8.43 kg) – participated in a crossover randomized study. They were asked to perform a 30-s Wingate test during six experimental sessions (three at 08:00 and three at 18:00 h) after different active warm-up (AWU) durations (5 min, 15 min, or 20 min). The AWU consisted of pedaling at a constant pace of 60 rpm against 50% of maximal aerobic power. Rate of perceived exertion (RPE) was recorded after the AWU and again immediately after the Wingate test. Heart rate and temperature (T) were recorded during each session at rest, after AWU and immediately at the end of the Wingate test. During the Wingate test, peak power (PP), mean power (MP), and the fatigue index were recorded. While the RPE estimations were higher in NTG, no time-of-day effect was recorded in either experimental group (morning or evening). T, PP, and MP were higher in the afternoon than in the morning (p < 0.001 for PP and MP; p < 0.05 for T). Similarly, PP and MP during the Wingate test were significantly higher in the TG than in the NTG (p < 0.001). The morning–evening difference of PP and MP was affected by AWU duration; AWU₁₅ was best in the morning for improving lower limb power for both the TG and NTG, whereas reducing this period to 5 min in the evening was appropriate for TG only.     

Evidence from a dual action of converting enzyme inhibitor on blood pressure in normal man

We studied the effect of a converting enzyme inhibitor (CEI), Captopril SQ 14,225 50 mg p.o. in eight supine normal subjects under a high sodium (150 meq/d) and low sodium (25 mEq/d) diet. On high sodium, plasma renin (PRA) and aldosterone were basal and Saralasin did not lower mean blood pressure. However, CEI induced an 11.4±3.2 mm fall in blood pressure (p<0.02) and either indomethacin 50 mg or ibuprofen 800 mg (PI), when given simultaneously on another day, abolished the blood pressure response (2.5±0.9 mm Hg, p>0.5). In contrast, on a low salt diet where renin was increased, CEI induced a drop in blood pressure which was not significantly altered by PI (12.8±1.1 vs. 10.0±3.1 mm Hg, p>0.5). CEI increased plasma renin on both diets (1.7±0.5 to 3.5±0.8 and 2.8±0.6 to 12.5±3.1 ng/ml/hr respectively both p<0.05). Aldosterone did not change (high Na⁺) or fell (low Na⁺). Inhibition of prostaglandin synthesis did not significantly block the renin rise from CEI suggesting that the direct angiotensin II negative feedback is relatively independent of acute prostaglandin release. Our studies suggest that CEI has a dual hypotensive action. In a low renin state, the hypotensive action appears to be mediated through vascular prostaglandins.     

A New Hand‐Held Indirect Calorimeter to Measure Postprandial Energy Expenditure

Objective: To verify the accuracy of a new hand‐held metabolic rate measuring device (MedGem) in quantifying postprandial energy expenditure (PP EE). MedGem measurements were compared to measurements obtained with a conventional indirect calorimeter (Delta‐Trac). Research Methods and Procedures: The resting metabolic rate of 15 healthy subjects was measured for 20 minutes using Delta‐Trac followed by a 10‐minute measurement period using MedGem. EE was again measured for 7 hours after consumption of a 2510‐kJ breakfast. Measurements were read from the Delta‐Trac for the initial 50 minutes of each hour followed by a single reading from the MedGem after 5 to 10 minutes of measurement. Measured EE was calculated as the average of the total measurement period for Delta‐Trac and for eight readings using MedGem; PP EE was calculated as the average of all measurements obtained after breakfast consumption. Results: There was no difference in resting metabolic rate between the two methods (6455.1 ± 417.6 vs. 6468.5 ± 337.2 kJ/d for Delta‐Trac and MedGem, respectively). Measured EE and PP EE values with Delta‐Trac (7019.1 ± 400.8 and 7099.8 ± 399.2 kJ/d, respectively) and MedGem (6775.6 ± 372.0 and 6819.5 ± 379.9 kJ/d, respectively) were not significantly different. There was no bias detected in any of the measurements made with MedGem compared with those of Delta‐Trac. Discussion: The new hand‐held EE measuring device can accurately track PP EE relative to a conventional indirect calorimetry system and, therefore, provides a new opportunity to assess PP EE in research settings and large‐scale trials.     

Responses of North American and New Zealand strains of Holstein-Friesian dairy cattle to homeostatic challenges during early and mid-lactation

This study investigated the physiological basis of differences in nutrient partitioning between the North American (NA) and New Zealand (NZ) strains of Holstein–Friesian cattle by determining the responses to homeostatic challenges at two stages of lactation. Glucose tolerance tests, epinephrine challenges and insulin challenges were carried out on consecutive days commencing on day 32 ± 0.48 (mean ± s.e.) of lactation (T1) and again commencing on day 137 ± 2.44 of lactation (T2). The insulin and non-esterified fatty acid (NEFA) responses to glucose infusion did not differ between the strains. The NZ strain had a greater clearance rate (CR) of glucose (2.04% v. 1.66%/min) and tended to have a shorter (34.4 v. 41.1 min) glucose half-life (t½) at T2 when infused with glucose. The NA cows had a greater glucose response to epinephrine infusion across T1 and T2, and tended to have a greater insulin response to epinephrine infusion. Plasma NEFA concentration declined to similar nadir concentrations for both strains at T1 in response to insulin, though from a higher basal concentration in NA cows, resulting in a greater (−2.29 v. −1.38) NEFA area under the response curve for NA cows. Glucose response to insulin varied with time, tending to be greater for NA at T1, but tending to be lower for NA at T2. The results indicated that NA cows had a greater glycogenolytic response to epinephrine, but both strains had similar lipolytic responses. The results also imply that higher basal circulating NEFA concentrations in the NA strain in early lactation were not due to diminished adipose tissue responsiveness to insulin. There were indications that glucose CR was greater in NZ cows in mid-lactation, and may form the basis of increased body tissue accretion during mid- to late-lactation in this strain.     

Insulin stimulation of Na/H antiport in L-6 cells: A different mechanism in myoblasts and myotubes

Insulin modulation of the Na/H antiport of L-6 cells, from rat skeletal muscle was studied in both myoblasts and myotubes using the fluorescent, pH sensitive, intracellular probe 2′,7′ bis (carboxyethyl)-5(6)-carboxyfluorescein. Insulin stimulated the Na/H antiport activity in L-6 cells, showing a bell-shaped dose response typical of other insulin responses: a maximum at 10 nM (ΔpH of 0.132 ± 0.007 and 0.160 ± 0.040 over basal value, for myoblasts and myotubes, respectively; means ± SD, n = 6–8) and smaller effects at higher and lower concentrations. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, also stimulated the antiport in myoblasts but not in myotubes. Surprisingly the rapid increase in intracellular pH was not observed when insulin and PMA were added simultaneously to myoblasts; apparently these two activators mutually excluded each other. Downregulation of protein kinase C, obtained by preincubation of cells with PMA for 20 hr, totally abolished both hormone and PMA effects in myoblasts, whereas in myotubes insulin stimulation was not affected. Inhibitors of tyrosine kinase activity, such as erbstatin analog and genistein abolished insulin effect on the Na/H antiport, both in myoblasts and in myotubes. Different sensitivity to pertussis toxin in the two cell types suggests that the differentiation process leads to a change in the signal pathways involved in the physiological response to insulin. J. Cell. Physiol. 171:235–242, 1997. © 1997 Wiley-Liss, Inc.     

Corticosteroid Modulation of Signal Transduction in the CATH.a Cell Line

Abstract: Noradrenergic neuronal networks originating in the locus coeruleus have been implicated in the stress response. In order to study this system in vitro, we have employed a locus coeruleus-like cell line, CATH.a, and have determined the effect of dexamethasone on receptor-mediated second messenger responses. The CATH.a cell line produced increases in intracellular cyclic AMP conversion in response to corticotrophin-releasing factor (EC₅₀ = 6.93 ± 1.26 nM, maximum conversion = 4.11 ± 0.20%) and vasoactive intestinal polypeptide (EC₅₀ = 240 ± 40 nM, maximum conversion = 8.92 ± 1.24%). Forskolin (10 µM) increased conversion from 0.48 ± 0.05 to 6.39 ± 0.38%. The α₂-adrenoceptor agonist 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK14304) inhibited the forskolin response with an IC₅₀ of 6.76 ± 0.11 nM. Carbachol increased total ³H-labelled inositol phosphate accumulation to a maximum of 3.01 ± 0.79 fold basal (EC₅₀ = 7.94 ± 0.14 µM). Bradykinin produced a maximum 1.81 ± 0.05 fold basal stimulation of phosphoinositide hydrolysis (EC₅₀ = 9.12 ± 0.16 nM). Both carbachol and bradykinin increased intracellular Ca²⁺ concentration probably via a combination of mobilisation of intracellular stores and gating of extracellular Ca²⁺. Incubation for 24 h with the glucocorticoid receptor agonist, dexamethasone (1 µM), significantly potentiated the receptor-mediated phosphoinositide responses to all the agents tested; however, of the receptor-mediated increases in cyclic AMP conversion, only the vasoactive intestinal polypeptide response was potentiated. These results show that the CATH.a cell line displays some of the properties expected of locus coeruleus neurons and that glucocorticoid receptor stimulation selectively modulates receptor-mediated increases in second messenger formation.     

β‐Cell Function Improvement After Biliopancreatic Diversion in Subjects With Type 2 Diabetes and Morbid Obesity

In subjects with obesity and type 2 diabetes mellitus (T2DM), biliopancreatic diversion (BPD) improves glucose stimulated insulin secretion, whereas the effects on other secretion mechanisms are still unknown. Our objective was to evaluate the early effects of BPD on nonglucose‐stimulated insulin secretion. In 16 morbid obese subjects (9 with T2DM and 7 with normal fasting glucose (NFG)), we measured insulin secretion after glucose‐dependent arginine stimulation test and after intravenous glucose tolerance test (IVGTT) before and 1 month after BPD. After surgery the mean weight lost was 13% in both groups. The acute insulin response during IVGTT was improved in T2DM after BDP (from 55 ± 10 to 277 ± 91 pmol/l, P = 0.03). A reduction of insulin response to arginine was observed in NFG, whereas opposite was found in T2DM. In particular, acute insulin response to arginine at basal glucose concentrations (AIR_basal) was reduced but insulin response at 14 mmol/l of plasma glucose (AIR₁₄) was increased. Therefore, after BPD any statistical difference in AIR₁₄ between NFG and T2DM disappeared (1,032 ± 123 for NFG and 665 ± 236 pmol/l for T2DM, P = ns). The same was observed for Slope_AIR, a measure of glucose potentiation, reduced in T2DM before BPD but increased after surgery, when no statistically significant difference resulted compared with NFG (Slope_AIR after BPD: 78 ± 11 in NFG and 56 ± 18 pmol/l in T2DM, P = ns). In conclusion, in obese T2DM subjects 1 month after BPD we observed a great improvement of both glucose‐ and nonglucose‐stimulated insulin secretions. The mechanisms by which BDP improve insulin secretion are still unknown.